Influence of Metal Additives on the Electrical Conductivities of the Oxide Ceramics as an Electrode Material

The electrical conductivities are reported for various oxide ceramics and cermets at 1000°C.Adding metal can greatly enhance the electrical condnctivities of the oxide materials.The conductivity of the ceramic added with metal depends on:(1)the conductivity σ_o of the oxides;(2)the content of metal additives;(3)the dispersion of the metal phase among oxide phase.The conductivity of the metal added does not affect the con- ductivity of the metal-containing ceramic.Although the metal-containing ceramic has much higher conductivi- ty than oxide ceramic,the change rate of their conductivities with temperature is similar and is controlled by E_g of the oxide.

Interfacial reaction between zirconium alloy and graphite mold/yttrium oxide ceramic mold

Zirconium alloys are active in the molten state and tend to react with the mold during casting. The casting technology of zirconium is not yet well established; especially in selecting the mold materials, which are diffi cult to determine. In the present work, the interfacial reactions between zirconium casting and casting mold were studied. The zirconium alloy was melted in a vacuum arc skull furnace and then cast into the graphite mold and ceramic mold, respectively. The zirconium casting samples were characterized using SEM, EDS and XRD with an emphasis on the chemical diffusion of elements. A reaction layer was observed at the casting surface. Chemical analysis shows that chemical elements C, O and Y from the mold are diffused into the molten zirconium, and new phases, such as ZrC, Zr3O, YO1.335 and Y6ZrO11, are formed at the surface. In addition, an end product of zirconium valve cast in a yttria mold has a compact structure and good surface quality.

Ab initio energetic study of oxide ceramics with rare-earth elements

Ab initio energetic calculations based on the density functional theory （DFF） and the projector augmented wave method （PAW） for determining the polymorphisms of lanthanide sesquioxides Ln2O3 （where Ln = rare-earth element, Y, and Sc）, LnMO3 perovskites （where M = AI and Ga）, and Ln2B207 pyrochlores （where B = Ti, Zr, and Hf） were reported. The relative lattice stabilities agreed well with the critically assessed results or the experimental results except the C-type Ln2O3 with a cubic structure, for which the calculated total energies were considerably more negative. With the increase of the Ln^3＋-cation radius, the polymorphic structures showed a degenerative tendency. The tendencies and quantities of the enthalpies of formation of the ternary oxide ceramics synthesized from their constituent binary oxides reasonably agreed with the available experimental results, and valuable thermodynamic properties were afforded to the compound, for which no experimental data is available. The enthalpies of formation of both perovskites and pyrochlores tend to become more negative with the increase of the Ln^3＋-cation radius.

Zero sintering-induced shrinkage of porous oxide ceramics

Porous oxide ceramics are widely used in extreme working conditions owing to their excellent resistance to high temperatures and corrosion.However,sintering is an inevitable process applied to ceramics,from the green body to the final product.The highly complex structures exacerbate the shrinkage-induced ir-regular deformation and crack formation in the sintering process.A pioneering approach is developed in this study to achieve zero shrinkage for porous alumina ceramics during multistep sintering,using a combination of active fillers-ZrAl 3 and Al 75 Si 25.The response surface method is used to optimize the material compositions and sintering process,to achieve shrinkages of less than 0.05%for the entire pro-cess.The sintering expansion mechanism is investigated by analyzing the pyrolysis and microstructures of samples at different temperatures.The combination of ZrAl 3 and Al 75 Si 25 can attain the continuous expansion of the matrix in a wide temperature range of 600-1400°C.Furthermore,typical alumina com-ponents are fabricated and used to verify the effectiveness of the proposed approach.Owing to shrinkage suppression,the profile deviation of the samples is less than 0.1 mm,and the proportion of microcracks is reduced by 97.8%.The suggested approach shows potential applications in near-net,low-defect fabrica-tion of complex fine ceramic components.

Laser melted oxide ceramics:Multiscale structural evolution with non-equilibrium features

Compared with the versatility in metal industry,application of laser on oxide ceramics is quite limited due to the intrinsic features of ceramics and limited understanding in laser-ceramic interaction mechanism,especially for high-energy laser that causes melting of materials.In this research,a study into general behaviors of several oxide ceramics melted by laser under inert atmosphere is presented.Key factors in determining state transformation,chemical reduction and phase structure are summarized,with further investigation into the evolution in microstructure at multiscale and the corresponding novelty and metastability.It is found that laser melting does show great potential in introducing deep reduction,unique microstructure,and notable increase in structure complexity and total entropy,and those features could contribute to some unconventional functional performance with brand-new structure-property relationship.

Ultrasonic investigations on elastic properties of (Bi,Pb)-Sr-Ca-Cu oxide ceramic superconductors

Ultrasonic velocities have been measured in single phase Bi_1.7 Pb_0.3Sr2CaCu2O8+x and Bi1.7Pb0.3Sr2Ca2O10+x polycrystalline samples. Anomalous changes of both longitudinal and transverse velocities were observed near 200K, which indicates that some structural phase transitio might occur. The elastic constants of these samples have been determined from the measured ultrasonic velocity data, which are much smaller than those of YBa2 Cu3 O7-y and BaTiO3, manifesting that the interlayer coupling will dramatically decrease when the c - axes of the unit cells of these perovstite-like multilayer ceramics increase. The values of Poisson ratio, however, of those ceramics are very close, implying similar interatomic bonding forces. Corrected to void-free state, the Debye temperature of these materials is estirnated as 270 ±20k. The temperature dependence of Debye temperatures for these materials is also calculated by using the same method and reported for the first time.

Spectral properties of Ce^(3+) doped yttrium lanthanum oxide transparent ceramics

Ce3＋-doped yttrium lanthanum oxide （Y0.9La0.1）2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce：（Y0.9La0.1）2O3 transparent ceramics are investigated. There appear two characteristic absorption peaks of Ce3＋ ions at 230~nm and 400~nm, separately. It is found that Ce3＋ ions can efficiently produce emission at 384~nm from （Y0.9La0.1）2O3 transparent ceramic host, while the emission is completely quenched in Re2O3 （Re=Y, Lu, La） host materials.

The Synthetic and Mechanical Properties of a Silica Matrix Cermet Composite

A cermet composite was prepared by employing thermal spraying flame onto stainless steel surfaces of(304)type.Hence 25,50%of aluminum was mixed with matrix of(10%Al_(2)O_(3)-SiO_(2)).A spray system consistis of oxygen barrel,acetylene and spray gun that contains powders feeder at different spray distances(5,10,15,20 and 25 cm).The thermal treatment of the samples resulting from spraying was performed at 1100℃for 1.5 hr.Some physical examinations(porosity and adhesion),mechanical tests(hardness and wear rate)and Atomic Force Microscope(AFM)test were performed before and after thermal treatment.The test results showed that the best mixing rate was(50%)and the best spray distance was(15cm)where the quality of coating layer improved after thermal treatment at 1100℃for 1.5 hr with a porosity ratio reduced from 11.2%to 6.6%,and adhesion strength improved with the increase in the alumina content to 50%.The results demonstrated that the best adhesion value after thermal treatment was 30.98 MPa.The hardness of coating layer increased from 45.78 to 54.88 HV;while the lowest rate of wear was at 50%of alumina with a spray distance of 15cm.Also,there was a clear improvement based on AFM within grain size,root mean square and roughness rate.

Preparation of large-size Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod by laser directed energy deposition and its microstructure homogenization mechanism

Laser 3D printing based on melt growth has great potential in rapid preparation of Al_(2)O_(3)-based eutectic ce ramics.In this work,la rge-scale Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod with diameter of 4-5 mm and height higher than 250 mm was additively manufactured by laser directed energy deposition.Especially,heat treatment was applied to eliminate the microstructure heterogeneity in the as-deposited eutectic ceramic,and the microstructure homogenization mechanism was studied in depth.The results indicate that colonies and banded structures completely disappear after the heat treatment,producing a homogeneous network eutectic structure.The microstructure homogenization is revealed to experience three stages of discontinuous coarsening,continuous coarsening and microstructure coalescence.Additionally,it is found that the eutectic spacing linearly increases with the heat treatment time,meaning that the coarsening behavior of the laser 3D-printed Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)eutectic ceramic satisfies well with the Graham-Kraft model.

A sol-gel method to synthesize indium tin oxide nanoparticles

Transparent conductive indium tin oxide （ITO） nanoparticles were synthesized by a novel sol-gel method. Granulated indium and tin were dissolved in HNO3 and partially complexed with citric acid. A sol-gel process was induced when tertiary butyl alcohol was added dropwise to the above solution. ITO nanopartides with an average crystallite size of 18.5 nm and surface area of 32.6 m^2 ]g were obtained after the gel was heat-treated at 700 ℃, The ITO nanoparticles showed good sinterability, the starting sintering temperature decreased sharply to 900 ℃, and the 1400 ℃ sintered pellet had a density of 98.1% of theoretical density （TD）.

Formation mechanism and roles of oxygen vacancies in melt-grown Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) eutectic ceramic by laser 3D printing

Laser three-dimensional(3D)printing has become a significant technique to fabricate high-performance Al_(2)O_(3)-based eutectic ceramics based on melt growth.However,oxygen vacancies are inevitable crystal defects during this process,and their formation mechanism and roles in the as-deposited ceramics are still unclear.In this paper,Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) ternary eutectic ceramics were prepared by laser 3D printing,and the formation mechanism of the oxygen vacancies was revealed by conducting a well-designed annealing experiment.In addition,the effects of the oxygen vacancies on the structure and mechanical property of the as-solidified eutectic ceramic were investigated.The formation of oxygen vacancies is revealed to be a result of the transfer of oxygen atoms from the oxide ceramic to the oxygen-deficient atmosphere by means of vacancy migration mechanism.Besides,the presence of oxygen vacancies has no obvious effects on crystalline structure and microstructure of the additively manufactured eutectic ceramic.However,the chemical bond property changes to some extent due to the formation of these crystal defects,which may affect the mechanical property of the as-deposited eutectic ceramic.It is found that the hardness decreases by 3.9%,and the fracture toughness increases by 13.3%after removing the oxygen vacancies.The results may provide a potential strategy to regulate the mechanical property of the oxide ceramic materials.

氧化锡陶瓷的飞秒激光3D非线性光刻

氧化锡是一种宽带隙半导体材料,广泛用于气体传感、光电和催化等领域.微米级至纳米级的复杂三维几何结构使传统的氧化锡陶瓷具有新的特性和功能.由于具有高的机械韧性和强度,陶瓷不易铸造或加工.增材制造为陶瓷材料灵活的几何造型带来了巨大的机会,但是极高的熔化温度使其在普通的3D打印方法上更加困难,而在微米或纳米尺度任意成形氧化锡陶瓷始终是一个挑战.本文中,我们利用在超快激光辐照下聚合的陶瓷前驱体,形成复杂且任意的3D陶瓷聚合物结构,通过煅烧处理后转变为具有均匀收缩率的高密度纯氧化锡陶瓷,特征尺寸可降至亚微米.透射电子显微镜(TEM)分析显示,氧化锡陶瓷纳米晶体的晶粒尺寸为2.5±0.4 nm.这项工作为制造精度高达亚百纳米的任意3D氧化锡陶瓷纳米结构提供了可能性,从而使其在不同领域更具应用前景.

Phase transformation of ZrO2 doped with CeO2

Thermal barrier coatings（TBCs） protection is widely used to prolong the lifetime of turbine components.The outermost layer of TBCs is ceramic layer, whose function is heat insulation, and the main composition of the ceramic layer is ZrO2. In this study, the micro-Zr02 and the nano-ZrO2 doped with 10 wt% CeO2 as well as microZrO2 and nano-ZrO2 were prepared by air plasma spraying（APS） to study the advantages of the addition of rare earth element. The effect of CeO2 on the phase transformation of ZrO2 was studied. The results show that there are few cracks in micro-and nano-ZrO2 doped with 10 wt% CeO2,and rare earth oxides can affect the phase transformation significantly. The morphologies, hardness and elastic modulus of the four ceramic layers were also discussed.